This invention relates to a method for inspection and fail-safe control of threaded joint tighteing processes as well as an apparatus for carrying out of said method.
In prior art indicating systems for this purpose, maximum and minimum limits have been set up to be compared with the actual torque and rotation values for a certtain joint at the end of the tightening. Indications have been made to show whether the final torque and rotation values of the actual joint are within the predetermined limits or not.
This type of indication suffers from drawbacks as not being able to show how the torque-angular displacement relationship has changed during the tightening process. As a matter of fact, there may occur faults in the threaded parts to be assembled that might impair the future strength and reliability of the joint but which happen to give favourable indications as regards the final torque and angular displacement values.
The main object of the invention is to check the torque values and angular positions of the joint against predetermined limits over the main part of the tightening process, thereby enabling premature discovery of faults in the joint that would result in a weaker joint when the tightening is completed or in damage to the parts being joined.
Other objects of the invention are to provide maximum and minimum limits of a wider fail-safe control range, and high and low limits of a narrower check range embraced by said wider control range, to use the limits of said control range to obtain a primary inspection of the tightening process and/or to accomplish a premature interruption of the tightening process in case the actual torque-angular position values get outside the control range, and to store the actual torque-angular position values and to check them later on against said narrower check range limits.